Long-range Attractive Potential Research Articles

Stability conditions for a boson system interacting with a partly repulsive and partly attractive potential

The properties of a dilute system of Bose particles with a short-range repulsive and a long-range attractive potential are studied. Some conditions on the scattering amplitude are found to assure the thermodinamic stability of the system. The method developed by Beliaev is used for calculating the ground-state energy and the elementary excitation spectrum of the system. The results are compared with those of Huang, Ezawa and Iordanskii and are found to be in complete agreement.

Sudden Approximation Applied to Rotational Excitation of Molecules by Atoms. I. Low-Angle Scattering

The sudden approximation is applied to the calculation of transition probabilities and cross sections for rotational excitation and scattering of homonuclear diatomic molecules by atoms. The present analysis is restricted to a consideration of the influence of the anisotropy and strength of the long-range attractive part of the interaction potential on the scattering at low angles. Nevertheless, the results illustrate the main features of the method applied to inelastic molecular collisions in general, and demonstrate its advantage over the first-order perturbation approximation. Measurements of low-angle differential inelastic scattering cross sections would yield directly the anisotropy of the long-range attractive potential.

Interaction Energies and Transport Coefficients of Li+H and O+H Gas Mixtures at High Temperatures

Accurate potential energy curves for the X 1Σg+, A 1Σu+, B 1Πu, and C 1Πu states of the Li2 molecule are calculated from observed spectroscopic data by the method of Rydberg—Klein—Rees (RKR), and compared with previous quantum-mechanical calculations, Long-range attractive potentials are estimated by extrapolation of functions fitted to the RKR ground-state curves of Li2, LiH, and OH. From these, the repulsive potentials derivable from interacting ground-state atoms are estimated semiempirically. Collision integrals are computed from the potentials, and transport coefficients of the gaseous systems Li+Li, Li+H, and O+H are calculated for temperatures of 1000° to 10 000°K. A surprising result is the extraordinarily large values of the collision inregrals for Li+Li (and Li+H) interactions, which result in unexpectedly small values of diffusion coefficient, viscosity, and thermal conductivity. For traces of Li in Li+H mixtures at low temperature, the thermal diffusion factor is very large. Various approximate formulas for viscosity and thermal conductivity of mixtures are seen to give poor agreement with exact calculations for the systems considered.

Velocity Dependence of the Differential Cross Sections for the Scattering of Atomic Beams of K and Cs by Hg

Measurements of the velocity dependence of the angular intensity distribution of potassium and cesium beams scattered by a crossed beam of mercury are presented. The alkali beam was velocity selected, with a triangular velocity distribution (half-intensity width 4.7% of peak velocity); the velocity was varied over the range 185–1000 m/sec. The Hg beam had a thermal distribution; the average Hg speed was ∼235 meters per second. The scattering data have been converted to the center-of-mass system. The angular distributions show the expected strong forward scattering and evidence the phenomenon of rainbow scattering. The energy dependence of the rainbow angle is used to evaluate the interatomic potential well depth, interpreted as the dissociation energy De of the 2Σ+ molecular ground state. Values (in erg×1014) thus obtained (±5%) are 7.46 for KHg and 7.72 for CsHg. Absolute values of differential cross sections could not be obtained; only relative cross sections D(θ) are reported. The observed low-angle behavior D(θ) ∝θ- 7/3 serves as direct experimental confirmation of the r—6 dependence of the long-range attractive potential for K–Hg and Cs–Hg systems.